Process of making tanninlike materials and the resulting products



Patented Apr. 27, 1954 PROCESS OF MAKING TANNINLIKE MATE- RIALS AND THE RESULTING PRODUCTS Shutung Tu, Racine, Wis.','.assignor to Tane'xco,

Inc., a corporation of Delaware No Drawing. Application January 31, 1950, Serial No. 141,590

2 Claims. (Cl. 260-4735) This invention relates to a method of making tannoid materials and the resulting products, and more particularly to the extraction of protannin materials, and the conversion of these materials in the presence of sulfur dioxide under pressure into tannin materials. The term protannin is herein defined to cover materials of the character usually associated in nature with tannin but having little or no normal ability to tan leather, but which are convertible by The redwood tree, of course, contains tannin as well as the protannin materials. Tannin content is, however, normally so low as to make its extraction from this wood uneconomical. Tannin contents as high as 12% have been reported from redwood, although the usual amount is nearer 2%.

The processes of the present invention essentially comprise three steps, which, however, need not be necessarily sequentially made in a given operation. The first step is the extraction of the protannin, which need not be separated from any tannin present. This is readily accomplished by the use of any leaching process with a small amount of alkali. The step of extraction per se is no part of the present invention, but its control is new.

Normally caustic soda is used as the alkali. For example, an aqueous solution content from 0.5 to 1.5% NaOI-I on the weight of the wood under a pressure of upwards to 5 pounds per square inch gauge, and at the corresponding temperature is suitable. Obviously other alkalies such as ammonium hydroxide may be utilized instead. The pressure with ammonium hydroxide will, of course, need to be somewhat higher to give the same temperature. The amount of alkali required depends upon the character of the wood material undergoing treatment as well as upon the tannin content thereof. Rootwood requires more caustic soda than the average, while stump wood, conveyer waste and headrig sawdust do not require so high a percentage of alkali. The protannin material, particularly if colored, is reduced by the treatment. Inasmuch as the sulfur dioxide used in the next step is a reducing 2 agent, no separate reduction is necessary, but a separate reduction may be made if desired.

The amount of alkali employed is as little as will operate eihciently, inasmuch as one of the prime values of the present process is the substantial absence of salts in the final product. It is, therefore, important that the metal ion content in the extract be at a minimum at the commencement of the conversion process.

Normally one hour is used foreach extraction. This, however, was on a batch system, and the time can be reduced by the use of countercurrent flow.

The amount of water does not appear to be particularly important within the normal range of about 5 to 2.8 milliliters of water to a gram of wood. The preferred pH range at the conclusion of the operation is between 6.0 and 8.5. If the pH is 6.0 or less, neutralization with S02 before concentration to the point where pressure 502 treatment is given is not necessary. If the pH is above 6.0, the liquor is neutralized with S0;

to a pH of 6.0 before preliminary concentration.

It has been found that sodium carbonate or other alkali metal carbonates may be used with advantage as the alkaline extraction medium. Enough of the material is used to reach the desired pH. On addition of the S02 at least a part of the carbonate reacts to form carbon dioxide, as a result of which less S02 is required in the reaction. This reduces oxidation during the preliminary concentration.

It is important that the amount of sulfur dioxide used is low only so that decomposition of the products will not occur. In this respect the process involves quite diiferent conditions than those encountered for instance in the paper pulp manufacture, where it is desired to secure docomposition and decomposing proportions and temperatures are employed. As is well known, the waste liquor from the sulfite of pulp conversion has proved of little value for tanning purposes.

After concentrating to 15-20% total solids, the liquor is treated with S02 to pH 4. It has been found that best results are obtained when the amount of S02 employed is only sufiicient to produce a pH within a range of 4 to 5. While it is possible to go slightly below a pH of 4 with good results, the greater the addition of S02, the more chance there is of some decomposition, and it is, therefore, preferred not to stop substantially at pH 4.

As acidification occurs, the metal ion is, of course, converted to the sulfite and/or bisulfite.

ceptable color. The shrinkage temperature of such leather was about 7 5 C.

The exact nature of the chemical change occurring is not understood, but it is believed that the sulfur dioxide does have a sulfonating effect on the protannins.

The following table presents examples of the processes hereinbefore described:

Rootwood Stump Wood Sawdust Conveyor Waste Quantity of wood on a dry basisw- 5,000 gr 5,000 gr. Amount of Water 25,000 25,000 cc. Alkali as NaOH 70 Pressure Time pH coming out of extra Concentrated to Evaporation desired.

0O Upwards to hours. 50% solids or dry as 1 hr -I 1 hr 50% solids or dry measure of the acidity of the system. The true equilibrium pH, as indicated after treatment, is approximately 5.

Any gummy residue which may be formed may be readily separated by decantation of centrifuging if desired.

The sulfite conversion process is preferably carried on at a temperature of 150 C. under the corresponding pressure. The time required varies with the character of the material undergoing treatment. Redwood and like materials require a period of upwards to two hours for best results. The rootwood of the redwood tree on the other hand requires a longer time. In any case, too short a period will result in poor or incomplete conversion, While too long a. period of time produce more insolubles.

The concentration of the liquor employed is preferably about -20% solids during the sulfiting operation.

The resulting aqueous product may be evaporated to dryness, or it may be evaporated only sufliciently to concentrat the material. Insolubles may readily be removed by centrifuging, filtering or decantation. The product may also be produced by spray drying.

The product may be used for tanning leather in the same manner as ordinary tannin, and produces a satisfactory tamied product with ac- The foregoing detailed description is given for clearness of understanding only and unnecessary limitations should not be understood therefrom as modifications will be obvious to those skilled in the art.

I claim:

1. The method of converting vegetable materials bearing materials capable of conversion to tannin-like material having the property of reacting with animal skins to form leather, which comprises: extracting the vegetable material with an aqueous solution containing an amount of alkali sufficient to produce an extract having a pH of about 6.0 to 8.5 and then adding an amount of sulfur dioxide sufiicient to reduce the pH but not substantially below 4 and heating under pressure to produce a temperature not greater than about C. to produce a tannin-like material from such vegetable material.

2. Tannin-like material produced by the meth- 0d of claim 1.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,505,818 Williams et al May 2, 1950 FOREIGN PATENTS Number Country Date 414,799 Great Britain Aug. 16, 1934 50% solids or dry. 

1. THE METHOD OF CONVERTING VEGETABLE MATERIALS BEARING MATERIAL HAVING THE PROPERTY OF RETANNIN-LIKE MATERIAL HAVING THE PROPERTY OF REACTING WITH ANIMAL SKIN TO FORM LEATHER, WHICH COMPRISES: EXTRACTING THE VEGETABLE MATERIAL WITH AN AQUEOUS SOLUTION CONTAINING AN AMOUNT OF ALKALI SUFFICIENT TO PRODUCE AN EXTRACT HAVING A PH OF ABOUT 6.0 TO 8.5 AND THEN ADDING AN AMOUNT OF SULFUR DIOXIDE SUFFICIENT TO REDUCE THE PH BUT NOT SUBSTANTIALLY BELOW 4 AND HEATING UNDER PRESSURE TO PRODUCE A TEMPERATURE NOT GREATER THAN ABOUT 150* C. TO PRODUCE A TANNIN-LIKE MATERIAL FROM SUCH VEGETABLE MATERIAL.
 2. TANNIN-LIKE MATERIAL PRODUCED BY THE METHOD OF CLAIM
 1. 